1. Field of the Invention
The present invention relates to a chair which a backrest can be inclined backwards.
2. Description of the Related Art
A chair which a backrest surface is arranged by bridging an upholstery member between frame elements that comprise a pair on the right and left sides is conventionally disclosed. For instance, there is disclosed a chair arranged in that an upper portion of the backrest surface is supported by an upper frame element while a lower portion of the backrest surface is supported by the lower frame element, wherein each of the upper frame element and the lower frame element is individually made to perform rotating operations around a horizontal axis, that is, rocking operations (see, for instance, Japanese Patent Laid-Open Publication No. 2002-119375 and Japanese Patent Laid-Open Publication No. 2002-119373). With this arrangement, such chairs realize the backrest surface that suits trunks or backbone shapes of individual seating persons and that further might follow movements of upper bodies of seating persons.
Incidentally, when a person takes seat on a chair in a condition in which the upper body is erected, the person often turns back, reaches his or her hand or twists his or her body. The chairs according to the above-mentioned patent documents were arranged in that they followed movements of the upper body, and particularly the upper portion of a seating person by rocking the upper frame element with respect to such movements of the seating person.
However, when the seating person inclines his or her upper body backwards, the backrest is required to reliably support the upper body of the seating portion. More particularly, when the upper frame element of the backrest is movable in accordance with movements of the upper body of the seating person as discussed above, it will in turn be impossible to support the upper portion of the upper body in a stable manner. Such an arrangement will cause a drawback in that the seating person might feel unstable when he or she inclines his or her upper body to incline the lower frame element of the backrest backward.